My passion for firearms started young. As a small kid, I was always interested in firearm design, mechanisms, history, and operation. Obviously, that passion has now grown humbly into a profession that I enjoy daily. My first entry into the “professional” realm was assisting a small gun store in my hometown with internet sales of firearms and their accessories. It paid $10 per listing but that was normally compensated through store credit.
While in the shop one day, we received a shipment from CMMG of a new product they’d just released: a .22 Long Rifle conversion kit for the AR-15 platform. The kits included a 25-round magazine and seemed to be a cost-effective alternative for practicing with an AR-15. At the time, .223 ammunition was a little over $200 for 1,000 rounds while .22 LR ammunition was about $40 for 1,000 rounds. The .22 LR kit cost less than $200 and pays for itself in less than 1,000 rounds.
Since that purchase, I’ve shot a lot through my .22 LR conversion kit (I would estimate at least 10,000 rounds through the original kit). I’ve acquired two more conversion kits since then and still use them for training to focus on skill-building while keeping ammo costs low. With ammo prices still expensive, it’s a great tool for novice and advanced shooters alike. While the CMMG .22 conversion kit is nothing new, I’ve learned some do’s and don’ts from having so much trigger time on the kit and thought it worthwhile to share this information for those who are new to the system or interested in purchasing one.
The CMMG .22 Conversion Kit
Early versions of the CMMG .22 conversion kit are a far cry from where they are today. Undoubtedly, CMMG has learned from their own research and customer feedback what needed to be improved on the system. Early versions of the kit had a black phosphate finish and had some break-in period. The current kits have a smooth chrome-like finish that requires minimal lubrication or break-in.
The original CMMG kits shipped with Black Dog Machine magazines and went through several iterations. CMMG currently offers their own magazine. I personally don’t have experience with these newer magazines as my current ones have performed reliably for over a decade.
CMMG offers several enhancements for their .22 conversion kits. A forward assist option is available that allows the user to push the bolt forward should it not fully seat the round. In my experience, this is not an issue and I currently don’t use it on any of my conversion kits. While nice to have, it’s not a must-have for using this system. CMMG also offers an auto sear conversion that adapts the .22 conversion kit to full auto. In use with full auto rifles, this system can work very well and has an incredibly high cyclic rate. I would estimate in excess of 1,000 rounds per minute. It still makes me giggle to shoot the kit in full auto lowers as it sounds like a .22 mini gun. Unfortunately, I have had issues with the full auto kit recently but attribute this to the introduction of the Geissele SSF trigger I recently added to my full auto lower.
Installation and Maintenance
The CMMG kit is relatively easy to install. Remove the standard AR bolt carrier and replace it with the .22 conversion kit. The conversion kit features a chamber shaped like a .223 casing to adapt it to the AR platform. Close the upper and lower back together and the system is ready to run. No other components need to be swapped.
There is no last shot hold open as the magazine follower is what locks the bolt to the rear. The follower is easily identifiable and lets you know the firearm is empty. Once the magazine is removed, though, the bolt will close. I recommend keeping a chamber flag with the file to keep the bolt open for safety. The operation of the conversion kit is the same as a standard AR platform. The charging handle still charges the weapon to load a round into the chamber. The kit is basically plug-and-play.
For day-to-day maintenance, the gun should be cleaned thoroughly after each use. .22 Long Rifle is inexpensive but it’s also dirty. After a few hundred rounds, the interior of the upper receiver will be coated in residue and somewhat gritty. As a matter of routine, I will fire a magazine of .223 through the rifle after a .22 range session to verify there is nothing obstructing the operating system (whether direct impingement or piston). The CMMG .22 conversion kit uses direct blowback to function. Since .22 is a lower-pressure cartridge; carbon, unburnt powder, etc. build up around the gas block. Firing the higher pressure .223 will burn off some of this gunk while function-checking the firearm.
I recommend cotton swabs, old toothbrushes, gun solvent, and scrap towels or cloths to detail clean the rifle. This is especially important if converting back to .233 and you plan on using the rifle in a defensive or professional capacity. An AR chamber brush will remove build-up in the chamber and locking lugs. This area tends to collect a lot of debris because the kit doesn’t fill the breech face or chamber toward where the locking lugs engage. A thorough cleaning of the chamber and breech is a must after each range session.
Inspect the barrel for any build-up of lead or copper as the slower velocity rounds cause additional barrel fouling — especially if you’re using lead. As a matter of experience, copper-jacketed .22 performs better in .22 conversion kits and reduces fouling. Some years ago, a friend borrowed my conversion kit. After several hundred rounds of lead nose through it, the gas port on the rifle was fouled and the chamber had a build-up of lead around the throat. As a result, the rifle wouldn’t chamber a .223 round. After a thorough cleaning, the rifle was operational again.
After each shooting session, inspect the conversion kit for any damage or wear. My first kit was accidentally dropped on the back side on concrete. This cracked the weld on the back of the kit and, after some welding on my end, was fixed. Amazingly the kit ran fine, even with the loose back plate on the conversion kit. I highly recommend inspecting the exterior of the conversion chamber for stress cracks or wear. I’ve experienced two cracked chambers on the conversion kit after extensive use over nearly 13 years on two separate kits. While they still fired, the fouling of the AR’s chamber, throat, and barrel was problematic for cleaning. I have to commend CMMG’s customer service, as a quick phone call and a couple of emails had me with new chambers from them.
Operation and Ammunition Considerations
The current coating on the CMMG conversion kit is slick and doesn’t need large amounts of oil to function. CMMG recommends 36-grain bullet weights with their conversion kits and I tend to agree with their recommendation. Subsonic bullets are not recommended. High velocity .22 Long Rifle will function more consistently than standard velocity or subsonic ammunition. Personally, I haven’t seen issues with reliability using 40 or 36-grain ammunition.
The majority of malfunctions experienced with the .22 conversion kit are due to lower-quality standard velocity ammunition. For instance, Remington Golden Bullets never ran reliably with any of my kits. Others may say differently, but my experience has not been the best. Lead nose, subsonic, and similar loadings perform inconsistently.
If malfunctions are experienced, I recommend keeping a small knife or flat-edged tool to pop cartridges out of the chamber or from the internal operating mechanism. While this conversion kit works well, it is a .22 rimfire chambering and converts a design for full-power bottleneck rifle cartridges into a rimfire offering. Expect malfunctions as a tradeoff for cheaper ammunition costs.
I’ve run this kit with a multitude of triggers. Rock River two-stage, Geissele, BCM, and several other triggers have performed fine with this kit. However, be aware that the hammer can cause some performance issues. If the kit has issues with cycling with quality ammunition, try it on a different trigger group to see if that’s the issue.
An additional consideration with the CMMG .22 conversion is accuracy. Most AR pattern rifles have a 1:7” twist rate while rifles chambered in .22 Long Rifle are around the 1:16” range. Don’t expect precision groups with this conversion kit. Nevertheless, the reduced cost, light recoil, and low muzzle report are tremendous benefits.
The CMMG .22 Long Rifle kit has come a long way over the last 13 years and has left me impressed. For a quick conversion to train cheaply on your normal AR platform, it’s the best I’ve found to date, and I highly recommend it. With ammunition costs fluctuating manically over the last few years, adding this kit to your collection serves only to improve your skillset and get you on the range with less of a hit to the pocketbook.
